The present invention is related to a method of preparing particles such as nanoparticles having a controllable anisotropic property and devices including such particles. The invention finds particular application in conjunction with anisotropic nanoparticles such as quantum dots in liquid crystals, nonlinear optics, optoelectronic devices, solar cells, photocatalysis devices, photodegradation devices, nanolasers, computing devices, photoluminescence (PL) devices, electroluminescence (EL) devices, H2 generators, liquid crystal displays, one-dimensional semiconductor nanostructures, chromogenic smart devices, optical switches, filters, integrated photonic devices, power conserving LCD devices, power-consuming reflective displays, backlit displays, cell phone displays, intensity-controlled switchable windows, traffic lights using reflective liquid crystal panels, and spatial light modulators, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
Among different nanometer-scale particles, the preparation and the characterization of semiconductor particles represents an important field due to their potential utilization in nonlinear optics, optoelectronic devices, solar cells, in photocatalysis and in photodegradation (used in environmental protection technologies). Several methods have been used to synthesize suitable particles in situ based on systems such as reverse micelles, Langmuir-Blodget films, clay minerals, multi-walled carbon nanotubes, microemulsions, polyelectrolyte/surfactant complexes, ordered polypeptide or other organic matrices, hydrated derivates of polysaccharides prepared from bacteria, and uni- and multilamellar vesicles as reaction mediums.
Due to its optimum characteristics, CdS is the most often studied and described among many semiconductor nanoparticles. Unilamellar vesicles (liposomes) consisting of natural or artificial amphiphilics are ideal systems for the synthesis of CdS nanoparticles, because the versatility of the bilayers provides many possibilities for both particle size and shape modification, as disclosed in Y.-M. Tricot, J. H. Fendler, J. Phys. Chem. 90, 3369 (1986), B. A. Korgel, H. G. Monbouquette, Langmuir 16, 3588 (2000). The aqueous cores of the vesicles, because they behave as nearly spherical nanoreactors, provide a place for a chemical reaction resulting in solid nanoparticles. Recently, A. Bóta et al. have pointed out that the aqueous holes between the stacks of bilayers inside multilamellar vesicles are also adequate reaction compartments for the preparation of CdS nanoparticles. A. Bóta, Z. Varga and G. Goerigk: Biological systems as nanoreactors: anomalous small-angle scattering study of the CdS nanoparticles formation in multilamellar vesicles, Journal of Physical Chemistry B, 111 (2007) 1911-1915.
Divalent metal ions such as Cd2+ cause significant destruction in layer arrangement of these vesicles and at the same time the formation of domains rich in Cd2+ ions can be observed. These domains, with a characteristic size in the range of several hundred Å, are embedded inhomogeneously between the bilayers of vesicles. By adding an adequate reagent such as (NH4)2S to the system, the multilamellar structure is reconstructed significantly. As the collapse of gaps filled with Cd2+ ions occurs, compact small (CdS) particles are formed. The characteristic size of these particles falls into the range of approximately 5-10 nm. This procedure contains two critical points: first, the water-soluble metal ions form domains having a critical maximal size and an adequate metal concentration, which strongly determine the size of the resulting nanoparticles. Secondly, each domain results in the formation of one nanoparticle after the addition of reagent. The schematic procedure of making nanoparticles in lyotropic liquid crystals is shown in FIGS. 1a, 1b and 1c. FIG. 1a shows a lipid-water (l-w) system with bilayers of vesicles (the curved lines). FIG. 1b shows an l-w system with domains (dotted egg) rich in metal ions. FIG. 1c shows an l-w system with nanoparticles formed (solid oval).
Many other methods have also been used to prepare CdS nanorods and nanowires, such as a vapor-liquid-solid process, a thermal evaporation method, a template method, and an aqueous-solution process. In the past years, the hydrothermal method has been expanded to synthesize 1D nanostructures by solvothermal and hydrothermal microemulsion methods. Recently, it was shown that lyotropic columnar liquid crystalline materials can also act as a growth medium to optimize the size and shape of the semiconducting nanorods. The fabrication of CdS nanorods in PVP fiber matrices by electrospinning has also been reported. However, there remains a need to further simplify the methods and reduce the costs for synthesis of particles such as semiconducting nanoparticles.
Advantageously, the present invention provides a method for preparing anisotropic particles, such as semiconductor nanoparticles, and further provides various industrial applications of such anisotropic particles, exhibiting numerous technical merits such as a simplified and more controllable procedure, and cost-effectiveness, among others.